The present invention relates in general to power transfer and more specifically to a battery transfer circuit for powering an electronic device during operating and power failure conditions.
There are many prior art circuits that provide power to an electronic device when a connected power supply experiences a power failure or disturbance. When the power failure occurs, a battery, located within the electronic device, provides backup power to the electronic device. Although the battery is used to provide backup power, prior art circuits are unable to inhibit unwanted battery operation. Unwanted battery operation occurs when the battery supplies power to the electronic device during normal operating conditions due to load and line regulation characteristics of the wall-adapter or transformer-type power supply.
The present invention is directed at a battery transfer circuit for powering an electronic device and charging an internal battery from a power supply during normal operating conditions and for providing back-up power from the internal battery to the electronic device when a power failure or disturbance condition is sensed. The present invention is also easily adaptable to different power levels and provides a configurable output voltage threshold for battery operation as a result of the power failure to prevent unwanted battery operation due to line and load regulation characteristics of the power supply.
Another advantage of the circuit of the present invention is that it provides an instant transition from power supply, or normal, operation to battery, or power failure, operation without transfer circuit delays to overcome an electronic device reset due to the voltage drop-out experienced during a power failure. Also, the present invention provides a means for increasing battery run time during power failure operation by switching out series elements between the battery and the electronic device during a prolonged power failure.
The present invention also includes circuitry to sense the output voltage of the power supply to determine when a power failure or disturbance occurs.
According to an aspect of the present invention there is provided:
A battery transfer circuit connected to a load, a power supply for powering said load with at least a minimum supply voltage during normal operating conditions, and a source of battery voltage for powering said load during a power fail condition when said power supply is unable to power said load at said minimum supply voltage, said battery transfer circuit comprising:
a first circuit for applying at least said minimum supply voltage to said load during said normal operating conditions;
a second circuit for charging said battery to an optimal voltage greater than said minimum supply voltage and for down-regulating said optimal charge voltage to a predetermined voltage and for applying said predetermined voltage to said load during said power fail condition, wherein said predetermined voltage is less than said minimum supply voltage.